Sound recording compositions



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' Patented Nov. 19, 1940 I UNITED STATES PATENT OFFICE SOUND RECORDING COMPOSITIONS Arthur E. Schuh, Astoria, N. Y, assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application July 17, 1937, Serial No. 154,318

9 Claims. (Cl. 106-15) This application is a continuation in part of bined acids to combined acids is within a range an application filed on February 19, 1936, Serial of from .34 to .57. The ratio of the various con- No.64,721. stituents in these compositions is critical and This invention relates to a composition of matmust be obtained to secure satisfactory com- 6 ter or material suitable for use in the manufacpositions for high fidelity recording.

ture of sound records. These records are ordi- One composition in which the molar ratio of narily cut in relatively soft wax and the matefree to combined acid falls within the range of rial of the invention is wax-like in its physical from .34 to .57 and which has been found satischaracteristics. factory as a recording material is as follows:

10 An object of the invention is an improved wax- 10 like homogeneous, non-crystalline material hav- Example No. 1 ing a wrinkle-free surface, which is easily cut or engraved and which has the physical character- Percent istics necessary to retain the sound record cut or Grams y weight engraved in its surface. II

In accordance with the invention, this and Stearic acid 632 59.52

other ebieets are attained by forming a sound i niittioit saannasmaacommit: 31 recording material from metallic soaps of one or Basieleed bonate (2Pbo0i.Pb(0 84 7.98 more of the fatty acids to which there is added Abalyn (methylabletate) 15 a plasticizer, such as methyl abietate. The ratio T al 1061 100.00

of free acids to combined acids in the composition (2'34 lbs) is an important factor in determining the physical characteristics of the material, and, in accord- The monta-n Wax in the above formula is ance with the invention, this ratio is maintained known commercially as bleached montan within ath r close li it According to the literature, the amount of mon- 25 It has long been well known that materials for ta d in montan w x m va y m 50 t use in making sound recordings should hav 90 per cent montanic acid content. If the montirely different physical characteristics from matan Wax Varies in montanic acid content from 50 terials used in making duplicate records from to 90 per cent, the ratio of free to combined acid which the sound is produced, I general, th in the above formula varies from .41 to .49. The 30 materials for recording have been some form of stearic acid p y d s tr p s d mmerrather soft wax or wax-like material because of ciel steeric acid- In ascertaining e e to the ease with which the cutting tool can remove Combined acid ratio, it is assumed that s mil-- portions thereof to form the record. In fact, so terinl comprises 100 per cent Stearic acid common has the use of wax been for this purpose (CH3(CI'I 2)16COoH)- 35 that these materials and the wax recording itself The acid number of the montan wax is e e are commonly referred t a ably determined by the following method. Three It has been proposed in making the duplicate grams f m n a wax a d sp sed n approxirecords which are used for reproducing to comc y 25 c o ncrmal butyl a co l y ea .i bine with wax-like materials other materials de- The mixture is then cooled a 1 of ethyl signed to provide mechanical strength, moldabilalcohol are d. a d it is then efl ed until ity and a, resistance to wear or the abrasive acdissolved, after which the solution is removed tion of the reproducing sty1us In such matefrom the sourceof heat and. titrated with N/2 rials, it has been proposed to use metallic soaps, a co o c Potassium hydroxide using p such as stearates and palmitates of sodium and phthalein as an indicator. The acid number is 45 aluminum to which carnauba wax has been the number of milligrams of potassium hydroxadded, together with a small amount of ceresin. ide required to neutralize one gram of montan Such materials have been considered unsuitable wax. for recording waxes" because of their hardness. A montan wax having an acid numbe o 9.4

60 In accordance with this invention, homogeneas determined by this method has been found 0 ous compositions are prepared which are espesatisfactory when employed in the above decially desirable for use in high fidelity recording. scribed formula. The amount of montanic acid These compositions comprise a homogeneous disin the montan wax having an acid number of 79.4 persion of metallic soaps in an excess of longascribing to the montanic acid the formula chain fatty acids. The molar ratio of uncom- CH3(CH2)27COOH, is 62 per cent and the calculated ratio of free fatty acids, expressed as stearic acid, to combined fatty acids, expressed as stearic acid, is .43. The composition in the above formula, with a montan wax having an acid number of 79.4, has been found especially desirable for recording materials. In the event that the amount of montanic acid in the montan wax in the above formula is per cent, the molar ratio of uncombined to combined fatty acids is .47. While recording compositions having a free to combined acid ratio within a range as wide as .34 to .57 have been found satisfactory for recording purposes, it is preferred to employ compositions in which the ratio of the free to combined acids is between .38 and .48.

Examples of compositions which were found to represent the extreme limits of the ratio of free to combined acids are as follows:

Instead of the sodium and lead salts employed in the above examples, similar salts or other soapforming metals, the anion reaction products of which are volatile or the more reactive metals by themselves such as aluminum, zinc, etc., may be used. However, the metal content of such salts of other metals, such as the other alkali metals, alkaline earth metals (calcium, barium, magnesium, etc.), or other metals such as aluminum, etc., must be substituted in stoichiometric proportions to fall within the above ratio, to make a satisfactory recording wax. For example, 9 grams of aluminum are equivalent to 23 grams of sodium or 103 grams of lead. Likewise, other waxes having a high acid value, such as carnauba wax, may be employed instead of montan wax. Instead of stearic and montanic acids, other monocarboxylic fatty acids may be used, preferably those having more than 12 carbon atoms such as palmitic, myristic, monodecanoic, etc. While a record composition can be made by using only one acid containing material and only one metallic soap, it has been found that a composition containing at least two fatty acids and at least two definite metal soaps thereof prevents subsequent crystallization of the record composition. The prevention of crystallization eliminates one common source of noise which is often present in recording compositions. This inhibition of crystallization is a result of steric hindrance of the molecules in the lyophilic colloid produced in forming compositions of this invention.

To make the surface of this composition suitable for record purposes, it is desirable to add a plasticizer and, for that purpose, there is added to the base mixture the above specified amount of methyl abietate. The amount of plasticizer added is critical, inasmuch as the cutting properties, as related to the temperature during cutting, are governed by the plasticizer. Other substances, such as sperm oil, ceresin, petrolatum, semi-drying oils, alkyl phthalates, such as dimethyl phthalate, and chlorinated diphenyls may be used as plasticizers. However, the esters of abietic or similar acids, such as methyl abietate, were found considerably more suitable owing to their wide range of compatibility and attendant wide cutting range. Methyl abietate has been found most satisfactory since it permits recording over a range of temperatures.

In preparing the material the ingredients are weighed out in the proportions noted and the carbonates are thoroughly mixed and placed in a drying cabinet for preheating and drying. It has been found that an improvement in the rate and smoothness of the reaction results if the particles of the carbonates are heated to about 175 C. The stearic acid and montan wax are melted together and preferably heated to 175 C. and the previously mixed and heated carbonates are added. While 175 C. appears to be the best temperature, the reaction can be satisfactorily carried on at temperatures from C. to 190 C. At this point, copious frothing takes place and considerable carbon dioxide is evolved. In about ten minutes the reaction will be found to have materially subsided and then the plasticizer, previously heated to the same temperature range, is added, after which the heating is continued for a few more minutes and the product is then ready for filtration and casting. During the entire reaction the temperature is preferably maintained at about C. By following the above procedure, the reaction is controlled, thermal decomposition reduced and a wax which is highly translucent when cold is obtained.

If the proportions of acids to carbonates are held to those above specified, the resulting product will include a certain amount of free or uncombined acids. Expressed in terms of stearic acid, the molar ratio of free to combined acids calculated on the base formulae without the plasticizer will be that noted in the respective formulae. If the product is to be suitable for use as a recording medium in the manufacture of sound records, the ratio is important and should not exceed the limits .34 to .57. Various other metals may be substituted in the formula for sodium or lead and other long chain organic acids for the stearic acid or the montan wax and if the ratio above stated is maintained, a base material having the desired homogeneity for a recording wax will result.

While preferred embodiments of this invention have been described, various modifications may be made therein without departing from the scope of the appended claims.

What is claimed is:

1. A composition for sound recording comprising, by weight, approximately stearic acid 60 per cent, montan wax 13 per cent, anhydrous sodium carbonate 5 per cent, basic lead carbonate 8 per cent and a plasticizer 14 per cent.

2. A material for sound recording comprising as major constituents stearic acid and montan wax, a portion of the free fatty acids of said stearic acid and said montan wax being com-' bined to form metallic soap and the molar ratio of the free fatty acids expressed as stearic acid in said material to the combined fatty acids expressed as stearic acid in said material being within the range of from .34 to .57.

3. A material for sound recording comprising as major constituents stearic acid and montan lUOu bUMrUDl I IUND,

COATING OR PLASTIC.

wax. a portion of the free fatty acids of said stearic acid and said montan wax being com bined to form metallic soap and the molar ratio of the free fatty acids expressed as stearic acid in said material to the combined fatty acids expressed as stearic acid in said material being within the range of .38 to .48.

4. A material for sound recording comprising as major constituents stearic acid and montan wax, a portion of the free fatty acids of said stearic acid and said montan wax being combined to form metallic soap and the molar ratio of the free fatty acids expressed as stearic acid in said material to the combined fatty acids expressed as stearic acid in said material being approximately .43.

5. A material for sound recording consisting of stearic acid, montan wax, sodium and lead soaps and not more than 16% of other ingredients, a portion of said stearic acid and said montan wax being combined to form metallic soaps of sodium and lead and the molar ratio of the free fatty acids in said material expressed as stearic acid to the combined fatty acids in said material expressed as stearic acid being within the range of .38 to .48.

\JUGI bH HUM 6. A material for sound recording comprising 57.6% to 61.9%, stearic acid 10.1% to 15.8% montan wax and a compatible plasticizer, a portion of the free fatty acid in said stearic acid and said montan wax being combined to form metallic soaps and the molar ratio of the free fatty acids in said material expressed as stearic acid to the combined fatty acids in said material expressed as stearic acid being within the range of .34 to .57.

7. The composition defined by claim 2 wherein methyl abietate constitutes substantially the remainder of said composition.

8. The composition of claim 6 wherein the compatible plasticizer is methyl abietate and constitutes substantially the remainder of said composition.

9. A composition for sound recording comprising, by weight, stearic acid approximately montan wax approximately 13%, anhydrous sodium carbonate approximately 5%, basic lead carbonate approximately 8% and methyl abietate approximately 14%.

ARTHUR E. SCHUH. 

